Surface SnO₂ Decoration: An economical and efficient alternative to Pt shells in Pt-Co catalysts for enhanced oxygen reduction reaction

Pt-metal alloy catalysts have been regarded as improvements over traditional Pt catalysts for the oxygen reduction reaction (ORR), but suffering from instability due to the increased oxophilicity and susceptibility to oxidation. To address this issue, two strategies, Pt shell and metal-oxide decoration, have been proposed for further enhancement of ORR performance. However, comparative studies investigating how these two strategies affect the electronic structure of active sites, including their structure evolution and redox capabilities during the ORR process, are relatively limited. In this study, we decorated commercial Pt₃Co catalysts with Pt shell (Pt₃Co@Pt) and SnO₂ species (Pt₃Co-SnO₂) to investigate their similarities and differences in electronic structures, dynamic evolutions, and underlying mechanisms of ORR active sites. Operando X-ray absorption spectroscopy (XAS) revealed that both strategies mitigated issues related to Pt oxidation, reaction hysteresis, and oxygen affinity in commercial Pt₃Co, with SnO₂ demonstrating even greater efficacy. The Pt₃Co-SnO₂ catalyst exhibited kinetic mass activities as high as 824 mA/mg_Pt with superior stability, markedly outperforming those of commercial Pt, commercial Pt₃Co, and Pt₃Co@Pt. Computational simulations further confirm that SnO₂ surface decoration effectively masks inactive sites with high oxophilicity on Pt₃Co for the excellent ORR activity, while accumulating negative charges from surface oxygen and mitigating phase segregation for enhanced ORR stability.